1. Field of the Invention
The present invention relates to a disc cartridge constructed so that disc access to a disc-shaped recording medium enclosed inside a cartridge main body is possible via a disc access opening.
2. Description of the Related Art
As one example of this type of disc cartridge, a disc cartridge where an information recording medium is enclosed inside a cartridge case is disclosed in Japanese Laid-Open Patent Publication No. 2003-123426. This disc cartridge includes a disc-like information recording medium, a cartridge case including an upper shell and a lower shell, an inner shell that functions as a disc tray, and a pair of shutter members (shutters) disposed between the inner shell and the lower shell. An opening for disc access to the enclosed information recording medium is formed in the lower shell, which is attached to the upper shell. A disc access opening is formed in the inner shell with the same shape and size as the opening of the lower shell, and the inner shell is rotatably enclosed inside the cartridge case so as to be sandwiched between the upper shell and the lower shell. By doing so, when the disc cartridge is loaded into and ejected from a recording/reproduction apparatus, the recording/reproduction apparatus rotates the inner shell with respect to the cartridge case so that part of the opening in the lower shell is opened and closed by the inner shell. In addition, a pair of support shafts for supporting the shutter members are provided so as to protrude on the inner shell.
On the other hand, bearing holes through which the support shafts of the inner shell are inserted are formed in the shutter members that are attached so as to be capable of rotation relative to the inner shell. When the disc cartridge is loaded into the recording/reproduction apparatus or ejected from the recording/reproduction apparatus, the shutter members are rotated relative to the inner shell by rotating the inner shell relative to the lower shell so that the opening in the lower shell is opened and closed by the inner shell and the shutter members. In this disc cartridge, a construction is used where end parts of the support shafts of the inner shell are crimped in a state where the support shafts have been inserted through the bearing holes formed in the shutter members to form expanded-diameter head parts, so that separation of the shutter members from the inner shell is prevented while rotation of the shutter members with respect to the inner shell is still permitted.
By investigating the conventional disc cartridge described above, the present inventors discovered the following problems. With the above disc cartridge, when the shutter members are attached to the inner shell, the expanded-diameter head parts are formed inside concaves formed in the rims of the bearing holes by causing thermal deformation of the end parts of the support shafts on the inner shell using a thermal crimping device or an ultrasonic processing device in a state where the support shafts have been inserted through the bearing holes of the shutter members (i.e., the head parts are formed by a crimping process). Here, when thermal deformation of the end parts of the support shafts is caused by a thermal crimping device, for example, it is necessary to control the temperature of the head molding tip (i.e., the part placed in contact with the end parts of the support shafts during crimping) to a suitable temperature for the crimping process. However, when continuously mass producing disc cartridges, it is difficult to always keep the head molding tip at a constant temperature, and therefore it is difficult to form expanded-diameter head parts of a uniform size.
More specifically, when the temperature of the head molding tip is too low, it is not possible to sufficiently heat the end parts of the support shafts when the head molding tip presses the end parts, so that the end parts do not thermally deform sufficiently and the diameter (size) of the expanded-diameter head parts formed inside the concaves is reduced. In this state, since the support shafts can easily come out of the bearing holes due to a shock caused by the disc cartridge being dropped, for example, the shutter members can easily become detached from the inner shell. On the other hand, when the temperature of the head molding tip is too high, the end parts of the support shafts thermally deform more than necessary when the head molding part forming tip presses the end parts, and although the formed expanded-diameter head parts are large, the thickness of the expanded-diameter head parts becomes too thin. In this state, the expanded-diameter head parts are easily broken, resulting in the shutter members becoming detached from the inner shell. Also, if the temperature of the head molding tip is even higher, when the head molding tip presses the end parts of the support shafts, thermal deformation occurs not only for the support shafts but also for the rims of the bearing holes, resulting in the shutter members being welded to the inner shell. In this state, rotation of the shutter members with respect to the inner shell is obstructed. In this way, in the conventional disc cartridge where the shutter members are attached to the inner shell by a crimping process where thermal deformation is caused using a thermal crimping device or the like (hereinafter simply referred to as “crimping”), it is difficult to keep the amount of thermal deformation suitable and uniform, so that there has been the problem that it is difficult to avoid detachment of the shutter members from the inner shell and poor rotation of the shutter members with respect to the inner shell.